The present invention relates to a process for purification of effluents.
Recently, water pollution such as eutrophication of inland seas, lakes, and marshes and pollution of rivers caused by industrial effluents have become significant problems.
Although industrial effluents are strictly controlled by environmental pollution control regulations, there are no regulations controlling small-scale household effluents. Recently, countermeasures for this form of environmental pollution and the development of effective effluent purifying processes have been desired. While there are various physicochemical treatment methods for effluents, biochemical treatment processes utilizing microorganisms have become of particular interest. Biochemical treatment processes are eliminating methods wherein mostly soluble organic matter, nitrogen, and phosphorus in an effluent are eliminated utilizing the action of microorganisms. It is generally divided into the activated sludge process, the bio-film process, and the oxidation-pond process. The bio-film process is one wherein a bio-film is adhered to the surface of a solid, and the bio-film decomposes pollutants in water and makes them harmless. This process can be subdivided into the following six processes:
(1) Trickling Filtration Process PA0 (2) Rotary-Disk Process PA0 (3) Fixed Bed Process PA0 (4) Tube Contacting Oxidation Process PA0 (5) Gravel Contacting Oxidation Process PA0 (6) Fluidized Bed Process PA0 1. Elutriation of bio-film-bearing particles is apt to occur, especially under a high load due to thickening of the bio-film. PA0 2. Oxygen deficiency tends to occur. PA0 3. A carrier particle for adhering the bio-film which is satisfactory with respect to specific gravity, strength, and cost has not been available.
Achieving a large purifying capacity of the bio-film process requires that the effective surface area of the bio-film be large and that the operation be stable.
Among the above six bio-film processes, the effective surface areas of processes (1) through (5) range from 40 to 500 m.sup.2 per m.sup.3, while that of the fluidized bed process reaches 3000-5000 m.sup.2, which is almost ten times those of the preceding five processes. Therefore, even small sized fluidized bed equipment can satisfy a comparatively large requirement with its great treating capacity per unit area of the bio-film.
However, even through the fluidized bed process has a large capacity for treating effluents, it has not been widely used in industry for the following reasons: